Re: Concorde's Engines

Date:         18 Jun 99 01:39:26 
From: (Wolfgang Keller)
Organization: Customer of UUNET Deutschland GmbH, Dortmund, Germany
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Gregory Travis <> wrote:

> How does the >INLET< produce thrust?

My fluid dynamics classes were quite some time ago, but something I
still remember is:

F = m_dot * (v_2 - v_1)

Where F is the thrust generated by some kind of air-breathing engine
(positiv in the direction opposite to v_1 and v_2), m_dot is the air
flow through the engine (approximation: fuel mass set to 0), v_2 is the
exhaust speed and v_1 the speed at the inlet.

Now, if we only take the inlet itself, v_2 is smaller than v_1, because
the air is slowed down. Thus, the inlet can not produce thrust, it
always generates drag. To generate thrust, you need to accelerate air,
not slow it down.


Wolfgang Keller

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